U.S. patent application number 16/780353 was filed with the patent office on 2020-06-04 for magnet arrangement for position sensor device and corresponding position sensor device.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Udo Ausserlechner.
Application Number | 20200176162 16/780353 |
Document ID | / |
Family ID | 53523209 |
Filed Date | 2020-06-04 |
United States Patent
Application |
20200176162 |
Kind Code |
A1 |
Ausserlechner; Udo |
June 4, 2020 |
MAGNET ARRANGEMENT FOR POSITION SENSOR DEVICE AND CORRESPONDING
POSITION SENSOR DEVICE
Abstract
A magnet arrangement including at least one magnetic element
providing a modulated magnetization in a first direction and an
essentially constant magnetization in a second direction different
from the first direction.
Inventors: |
Ausserlechner; Udo;
(Villach, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
53523209 |
Appl. No.: |
16/780353 |
Filed: |
February 3, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14935636 |
Nov 9, 2015 |
10553337 |
|
|
16780353 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01D 5/12 20130101; G01D
5/2451 20130101; H01F 7/021 20130101; G01R 33/022 20130101 |
International
Class: |
H01F 7/02 20060101
H01F007/02; G01D 5/12 20060101 G01D005/12; G01D 5/245 20060101
G01D005/245; G01R 33/022 20060101 G01R033/022 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2014 |
DE |
202014105652.1 |
Claims
1. A magnet arrangement, comprising: at least one magnetic element
providing a modulated magnetization in a first direction and an
essentially constant magnetization in a second direction different
from the first direction.
2. The magnet arrangement of claim 1, wherein the second direction
is essentially perpendicular to the first direction.
3. The magnet arrangement of claim 1, wherein the at least one
magnetic element comprises at least two magnetic stripes with
different magnetizations.
4. The magnet arrangement of claim 1, wherein the first and second
directions are straight directions.
5. The magnet arrangement of claim 4, wherein the at least one
magnetic element comprises a plurality of first magnetic stripes
having a first magnetization and second magnetic stripes having a
second magnetization different from the first magnetization, the
first and second stripes extending in the first direction and being
provided adjacent to each other in an alternating manner,
alternating between first and second stripes in the second
direction.
6. The magnet arrangement of claim 5, wherein a magnetization
direction of the first stripes differs from a magnetization
direction of the second stripes.
7. The magnet arrangement of claim 5, wherein a magnitude of the
magnetization of the first stripes differs from a magnitude of the
magnetization of the second stripes.
8. The magnet arrangement of claim 5, wherein a magnetization of
one of the first stripes or second stripes is zero.
9. The magnet arrangement of claim 5, wherein a width of the
stripes in the first direction varies monotonically in the second
direction.
10. The magnet arrangement of claim 5, wherein a width of the
stripes in the first direction decreases towards edges of the
magnet arrangement in at least one of the first direction and the
opposite direction of the first direction.
11. The magnet arrangement of claim 3, wherein the first and second
stripes are arranged in a spiral shape.
12. The magnet arrangement of claim 11, wherein a width of the
stripes decreases towards at least one of an inner end of the
spiral and an outer end of the spiral.
13. The device of claim 11, wherein the stripes with one rotation
of the spiral by 360.degree. change their distance to a center of
the spiral by approximately one period of modulation.
14. The magnet arrangement of claim 1, wherein the magnet
arrangement is arranged at an essentially circular shape, the first
direction forming an angle smaller than 15.degree. with a
circumferential direction, and the second direction forming an
angle smaller than 15.degree. with a radial direction.
15. The magnet arrangement of claim 13, wherein the modulation in
the first direction is an approximately sinusoidal modulation.
16. The magnet arrangement of claim 1, wherein the at least one
magnetic element is provided on a magnetically soft carrier.
17. A position sensor device, comprising: a magnet arrangement as
defined in claim 1, and a magnet field sensor movable relative to
the magnet arrangement.
18. The device of claim 17, wherein a movement direction of the
magnetic field sensor forms an angle smaller than 15.degree. with
the second direction.
19. The device of claim 17, wherein the relative movement is such
that a maximum range of movement covers one period or less in the
first direction of the magnet arrangement.
20. The device of claim 17, wherein the direction of the relative
movement is one of a circumferential direction or a linear
direction.
Description
TECHNICAL FIELD
[0001] The present application relates to a magnet arrangement for
a position sensor device and to a corresponding position sensor
device using a magnet arrangement.
BACKGROUND
[0002] To sense a position, in some applications, one or more
magnetic field sensors are used together with a magnet arrangement,
the magnet arrangement moving relative to the at least one magnetic
field sensor. For example, to determine an angular position,
so-called pole wheels may be used, which when rotating cause a
modulation of a local magnetic field, which is then sensed. Based
on this modulation, a speed may be determined, and by integrating
the speed, a position may be obtained. Similar arrangements may be
used to detect linear movements.
[0003] As with such arrangement the local modulation is periodic,
only a speed (for example rotational speed or linear speed) may be
obtained directly, and a position (for example angular position or
linear position) may be obtained only indirectly via integration of
the speed.
[0004] However, in some applications, it may be desirable to be
able to obtain a position directly.
[0005] It is therefore an object to provide magnet arrangement and
position sensor devices which in some cases may enable a direct
determination of position based for example on a sensed magnetic
field.
SUMMARY
[0006] A magnet arrangement as defined in claim 1 and a position
sensor device as defined in claim 17 are provided. The dependent
claims define further embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic view of a position sensor device
according to an embodiment.
[0008] FIG. 2 illustrates a magnet arrangement according to an
embodiment.
[0009] FIGS. 3A-3D illustrate various implementation possibilities
of the magnet arrangement of FIG. 2.
[0010] FIG. 4 illustrates an implementation example of a magnet
arrangement according to some embodiments.
[0011] FIG. 5 illustrates a magnet arrangement according to some
embodiments.
[0012] FIG. 6 illustrates a magnet arrangement according to further
embodiments.
[0013] FIG. 7 illustrates a magnet arrangement for an angular
position sensor device according to an embodiment.
[0014] FIG. 8 illustrates a magnet arrangement for an angular
position sensor device according to a further embodiment.
[0015] FIG. 9 illustrates a cross-sectional view of an angular
position sensor device according to an embodiment.
DETAILED DESCRIPTION
[0016] In the following, various embodiments will be described in
detail referring to the attached drawings. These embodiments are
given by way of example only and are not to be construed as
limiting. For example, while embodiments may be described as
comprising a plurality of features or elements, in other
embodiments some of these features or elements may be omitted
and/or may be replaced by alternative features or elements. In yet
other embodiments, additionally or alternatively additional
features or elements apart from the ones explicitly described may
be provided. Features or elements from different embodiments may be
combined with each other to form further embodiments. For example,
variations or modifications described with respect to one of the
embodiments may also be applicable to other embodiments unless
noted to the contrary.
[0017] Some embodiments use a magnetic field sensor moving relative
to a magnet arrangement. "Moving relative" as used herein may
indicate a movement of the magnetic field sensor, a movement of the
magnet arrangement or both. A magnetic field sensor as used herein
is not limited to any particular type of magnetic field sensor, but
may be implemented in various manners, for example as a Hall
sensor, for example a Hall plate or a vertical Hall sensor, or a
magneto resistive sensor using one or more magneto resistive
elements (for example using a giant magnetoresistive effect (GMR),
an anisotropic magnetoresistive effect (AMR), a tunnel
magnetoresistive effect (TMR) or a colossal magnetoresistive effect
(CMR). Magnetoresistive elements may for example be provided in a
full-bridge or half-bridge configuration to implement a magnetic
field sensor. Other conventional implementations of magnetic field
sensor may be used as well. A magnetic field sensor may comprise
one or more sensor elements, e.g. to sense field components in one
or more directions.
[0018] A magnet arrangement refers to a device or element
generating a magnetic field. Such a magnet arrangement may use one
or more permanent magnets and/or one or more electromagnets to
generate the magnetic field.
[0019] Turning now to the figures, FIG. 1 illustrates a schematic
representation of a position sensor device according to an
embodiment. The position sensor device of FIG. 1 comprises a magnet
arrangement 10 and a magnetic field sensor 11. Magnetic field
sensor 11 may move relative to magnet arrangement 10 in a direction
12 (represented by an arrow in FIG. 1). While direction 12 in FIG.
1 is represented as a straight linear movement direction, in other
embodiments, other movement directions are possible, for example a
circular movement in case of an angular position sensor device, or
any other movement. In embodiments, the movement may be a movement
along a predetermined movement path, for example the linear
movement direction 12 shown in FIG. 1 or a circular movement
direction. To perform the relative movement, magnetic field sensor
11, magnet arrangement 10 or both may move.
[0020] Magnet arrangement 10 may comprise one or more magnetic
elements and is configured to provide a modulated field in a first
direction 13, while the magnetic field provided by magnet
arrangement 10 is essentially constant in a second direction 14.
"Essentially constant" may imply that e.g. over a range of movement
of interest, the magnetic field does not vary by more than 5%, more
than 10% or more than 20%. On the other hand, in direction 13, a
change of magnetic field may be significantly greater. In
embodiments, the modulation in the first direction 13 may be a
periodic modulation or an essentially periodic modulation, but is
not limited thereto. In the embodiment of FIG. 1, where the
direction 12 (movement direction) is linear, direction 13 and 14
may be two linear directions perpendicular to each other.
[0021] In the embodiment of FIG. 1, direction 12 is a direction
closer to direction 14 than to direction 13. For example, an angle
.tau. between movement direction 12 and direction 14 in which the
magnetic field is essentially constant may be less than 15.degree.,
e.g. less than 10.degree., but is not limited thereto. In
embodiments, by such a choice when moving along movement direction
12 magnetic field sensor 11 experiences a slower modulation of the
magnetic field sensed compared to a modulation along first
direction 13. In some embodiments, this may be used for position
determination as for example a bijective relationship between
magnetic field sensed by sensor 11 and position of sensor 11 within
a certain movement range may be given.
[0022] The signal of magnetic field sensor 11 may then be evaluated
by a controller 15. For example, in embodiments based on the
magnetic field sensed by sensor 11 controller 15 may determine the
position of magnetic field sensor 11 relative to magnet arrangement
10.
[0023] It should be noted that in embodiments where movement
direction 12 is not a straight direction (for example is a
circumferential direction for angular position detection),
directions 14 and 13 may also be non-straight directions. For
example, in such embodiments second direction 14 may be close to
the circumferential direction, and first direction 13 may be close
to a radial direction.
[0024] The general techniques and principle illustrated above with
respect to FIG. 1 serve only as a brief overview over some concepts
applicable in some embodiments. More specific examples will be
described next with reference to FIGS. 2-9.
[0025] FIG. 2 illustrates a magnet arrangement 24 according to an
embodiment.
[0026] Magnet arrangement 24 comprises alternating magnetic stripes
20, 21 with different magnetizations. In a direction labelled y',
which is an example for the first direction of FIG. 1, this results
in a modulation of the magnetic field with a period .lamda.. In a
direction perpendicular to direction y' (labelled x') in FIG. 2,
the magnetic field is essentially constant (for example with a
variation less than 5%, less than 10% or less than 20% in a
movement range of interest explained later) within a certain area
determined e.g. by a size of the magnet arrangement 24. In a
direction perpendicular to x' and y' (z-direction) the magnetic
field generated by magnet arrangement 24 in embodiments decreases.
Magnetic stripes 20, 21 may for example comprise magnets of
different strength, different orientations etc. Examples for
magnetizations of magnetic stripes 20, 21 will be given later with
respect to FIGS. 3A-3D. Magnetic stripes 20 and 21 may for example
be permanent magnets, for example plastic-bound permanent magnets,
which may have a thickness of the order of 2 Millimetres and may be
mounted to a carrier. In some embodiments, the mounting may be made
using glue or other adhesives. In an embodiment, the carrier may
comprise a magnetically soft material, for example magnetically
soft sheet steel. Such a material in embodiments may amplify the
magnetic fields generated by magnet arrangement 24 on a side
opposite to where magnetic stripes 20, 21 are mounted to the
carriers. In other embodiments, other carriers may be used. In yet
other embodiments, instead of permanent magnets electromagnets may
be used.
[0027] Before explaining position determination and movement of a
magnetic field sensor relative to magnet arrangement 24 of FIG. 2
in some more detail, first with reference to FIGS. 3A-3D and FIG. 4
some example configuration for magnetic stripes 20, 21 will be
discussed.
[0028] In FIGS. 3A-3D, M.sub.z indicates a magnetization in the
z-direction (perpendicular to x', y' of FIG. 2), and this
magnetization is shown over the y'-direction of FIG. 2, i.e.
M.sub.z (y'). In FIG. 3A, as indicated by 30, stripes 20 may have a
magnetization in the positive z-direction, and stripes 21 may have
a magnetization as indicated by 31 in the negative z-direction, of
approximately the same magnitude as stripes 20.
[0029] In FIG. 3B, as indicated by 32 and 33, the magnetization of
magnetic stripes 20 is in the positive direction, while the
magnetization of stripes 21 is in the negative z-direction and has
a different magnitude compared to the magnetization of stripes 20
(in the example of FIG. 3B a greater magnitude, although in other
examples it may also be a smaller magnitude).
[0030] In the example of FIG. 3C, as indicated by 34 magnetic
stripes 20 may essentially be omitted (i.e. no magnetization),
whereas stripes 21 have a magnetization in the negative
z-direction. In other embodiments, stripes 21 may have a
magnetization in the positive z-direction.
[0031] In the example of FIG. 3D, magnetic stripes 20, as indicated
by 36, and magnetic stripes 21, as indicated by 37, both have a
magnetization in the negative z-direction, wherein the magnitudes
of the magnetizations of stripes 20, 21 differ from each other. In
other embodiments, both magnetizations may be in the positive
z-direction. While in FIG. 3 the magnitude of magnetization of
stripes 21 is higher than of magnetic stripes 20, in other
embodiments this may be the other way round.
[0032] FIGS. 3A-3D are merely some examples showing that different
approaches exist to providing a periodic modulation to the
magnetization and therefore to the magnetic field generated in
y'-direction.
[0033] In other embodiments, the magnetization change between
magnetic stripes 20, 21 may be gradual. An example for such a
gradual change is shown in FIG. 4. Here, areas 40 may correspond to
magnetic stripes 20, and areas 41 may correspond to magnetic
stripes 41. The arrows illustrate the behavior of a magnetization
vector {right arrow over (M)} varying along the y'-axis. As can be
seen, here the magnetization changes gradually in a periodic
manner. In some embodiments, the change of {right arrow over (M)}
may be such that M.sub.z has a sinusoidal periodic behavior in
y'-direction.
[0034] As can be seen from FIGS. 3A-3D and 4, a plurality of
possibilities exist in various embodiments to provide a magnetic
field modulated in the y'-direction. It should be noted that the
examples of FIGS. 3A-3B and 4 are not exhaustive, and constitute
merely some possible examples.
[0035] Returning now to FIG. 2, magnet arrangement 24 may for
example be used for a linear position sensor, where a magnetic
field sensor moves relative to magnet arrangement 24 in an
x-direction between a y-axis and a line 23. In other words, a range
of travel for the magnetic field sensor along the x-direction is
given by an arrow 22 in FIG. 2.
[0036] In embodiments, magnet arrangement 24 in the x-direction
covers the complete range of travel 22 and in particular may extend
beyond the range of travel 22 (in positive x-direction, negative
x-direction or both). In a direction perpendicular to the direction
of travel (y-direction of FIG. 2), magnet arrangement 24 may also
extend considerably, for example have a similar extension as in the
x'-direction, but may also be more limited in other embodiments.
Generally, a larger extension may lead to a more exact and/or
uniform periodicity and/or reproducible behavior of the magnetic
field over the range of travel of a magnetic field sensor, but may
also require a larger magnet and more space, which may increase
costs. Therefore, in embodiments, a balance has to be made between
a required accuracy and costs and size considerations.
[0037] To explain position determination using a magnet arrangement
like magnet arrangement 24 more clearly, for illustration purposes
it is first assumed that magnet arrangement 24 extends essentially
to infinity in positive and negative x-direction as well as
positive and negative y-direction. Under this assumption, a
magnetic field generated by magnet arrangement 24 of FIG. 2 has the
following properties:
[0038] It is periodic with a period length .lamda. in y'-direction,
and
[0039] it is essentially constant in x'-direction.
[0040] Furthermore, in embodiments as explained a sensor moves in
the x-direction, which forms an angle .tau. with the x-direction.
.tau. may be less than 20.degree., for example less than
10.degree., for example about 6.degree.. Other angles .tau. are
also possible.
[0041] If a magnetic field sensor moved in the x'-direction, the
sensor would sense essentially no change in the magnetic field. If
the sensor moved in the y'-direction, the sensor would sense a
periodic magnetic field with a period length .lamda.. In
embodiments, when a distance of the sensor from magnet arrangement
24 is not too small, for example at least .lamda./2 and this
distance (in the z-direction) is constant, the modulation may be
essentially sinusoidal.
[0042] In embodiments, using the magnet arrangement of FIG. 2 the
amplitudes of Bz (magnetic field in z-direction) and By' (magnetic
field in y'-direction) are essentially identical, this identity
increasing with increasing z coordinate. Furthermore, Bz and By'
with a magnet arrangement as shown in FIG. 2 have essentially a
phase shift of 90.degree. to each other. For example, one of Bz and
By' in the y'-direction may be proportional to to
cos(2.pi.y'/.lamda.), and the other one of Bz and By' may be
proportional to sin(2.pi.y'/.lamda.). This 90.degree. phase shift
and the at least approximately correspondence of the amplitudes of
Bz and By' lead to the following two properties:
(1) By'.sup.2+Bz.sup.2=const.sub.x, i.e. the sum of the squares of
the values of the two field components By' and Bz are independent
from the position in x-direction, and (2) By'/Bz'=const.sub.z,th,
i.e. the ratio of the values of the two field components By', Bz'
is independent from the position z of the magnetic field sensor
(for example an air gap between sensor and magnet arrangement 24)
and independent from a thickness th of the magnet arrangement (like
magnetic stripes 20, 21). This thickness th in embodiments may be
homogenous.
[0043] A magnetic field sensor like magnetic field sensor 11 of
FIG. 1 in an embodiment may for example sense Bz and By', for
example using two sensor elements, one for each magnetic field
component Bz and By'. In this respect, it is to be noted that many
conventional sensor techniques like Hall sensors or
magnetoresistive sensors are sensitive to a particular magnetic
field direction.
[0044] To determine a x-coordinate of the sensor, for example
within the range of travel 22, a ratio between Bz and By' (i.e.
By'/Bz or Bz/By') may be formed. Based on this ratio, y' may be
calculated, for example as arctan (By'/Bz), arctan being the arc
tangent function.
[0045] In some embodiments, the angle .tau. is chosen such that
over the range of travel in x-direction (for example range of
travel 22) the sensor moves only over one period .lamda. in the
y'-direction, as indicated by a line 25 in FIG. 2. Therefore, in
such embodiment, the y'-position may be unambiguously determined
for each x-position within the range of travel 22. Furthermore, the
y'-position has a fixed relationship with the x-position over the
range of travel 22, such that in this way the position of the
magnetic field sensor can be determined (via the angle .tau.).
[0046] It should be noted by that essentially by choosing the angle
.tau. accordingly, the range of travel 22 is increased compared to
the period .lamda., while the sensor still in the y'-direction
travels only one period .lamda., which allows an unambiguous
determination of the position in some embodiments.
[0047] When determining the x-position in this way because of (2)
above x is essentially independent from the z-position of the
sensor device. Therefore, the method is robust against variations
of z in some embodiments.
[0048] In other embodiments, instead of absolute values Bz, By' a
magnetic field sensor may sense gradients thereof in the
y'-direction, i.e. dBz/dy' and dBy'/dy'. The properties (1) and (2)
mentioned above also apply to the gradients. This may be easily
seen from the fact that when for example Bz is proportional to
cos(2.pi.y'/.lamda.), dBz/dy' is proportional to
sin(2.pi.y'/.lamda.), and corresponding relationships also apply to
By' and dBy'/dy', i.e. by using the gradients the sine and cosine
term are essentially exchanged. Therefore, the techniques discussed
above may also be implemented using the gradients. In some
embodiments, using the gradients has the advantage that they are
robust against homogenous disturbance magnetic fields (as the
gradient of a homogenous field is 0 and therefore does not
contribute).
[0049] It should be noted that the amplitude of the magnetic fields
Bz and By' decreases exponentially with a distance from magnet
arrangement 24, for example proportional to exp(-2.pi.z/.lamda.),
wherein z=0 may be at the side of magnetic stripes 20, 21 facing
away from the magnet sensor (for example at an interface between
magnetic stripes and carrier). Therefore, to obtain large magnetic
fields to be measured, a small value of z may be used. On the other
hand, a certain distance between sensor and magnet arrangement may
be required due to mechanical constraints, e.g. to prevent contacts
between sensor and magnet arrangement which may even lead to
damaging. In some embodiments, a z-position of the sensor is
selected to be smaller than 2.lamda.. In some embodiments, for
designing magnet arrangement 24, a minimum and a maximum value for
the z-position of the sensor may be determined based on constraints
regarding the design and constraints regarding the magnetic field
needed for an accurate sensing, and then A may be selected (i.e. a
width of magnetic stripes 20, 21 in the embodiment of FIG. 2 may be
selected). .tau. may then be determined based on a required range
of travel 22 and the selected .lamda..
[0050] As already mentioned, the magnetic field in the embodiment
of FIG. 2 is periodic in y'-direction. In embodiments, the
magnetization of the magnetic stripes 20, 21 may be sinusoidal (for
example as illustrated with respect to FIG. 4), which may lead to
the magnetic field being sinusoidal also for small values of z. In
other embodiments, other magnetizations, for example rectangular
modulations as illustrated in FIGS. 3A-3C or triangular shaped
magnetizations may be used. For a rectangular magnetization in some
embodiments a larger distance z (for example exceeding .lamda./2)
may be used to have an approximately sinusoidal behavior of the
magnetic fields By' and Bz. For smaller distances, Bz may have an
approximately rectangular shape and By' may have a triangular
dependency on y', which may make determination of an exact position
more difficult for small distances z. Other magnetizations may also
be used.
[0051] In the above explanations it has been assumed that the
magnet arrangement 24 has a large extension in the y'-direction,
which leads to a regular periodic dependency of the magnetic field
in y'-direction (for example sinusoidal dependency or approximately
sinusoidal dependency). In practical cases, as mentioned
previously, it may be desirable to limit the extension in
y'-direction due to area or cost constraints. With the regular
stripes 20, 21 of FIG. 2, such a limitation would lead to an
increase of the amplitude of the magnetic field and a variation of
the periodicity closer to the edges (left and right edges in FIG.
2) of magnet arrangement 24. The behavior of the magnetic fields in
this case is still similar to the sine or cosine curve, but the
amplitude increases with decreasing distance to the edges, and the
period of the modulation increases. This effect is also known as
"windowing". To compensate this, in embodiments the period .lamda.
of the magnetic stripes (e.g. width of stripes) may be decreased
closer to the edges.
[0052] A corresponding embodiment of a magnet arrangement 52 is
illustrated in FIG. 5. Here, a width of stripes 50, 51 and
therefore the period of the stripes decreases in the positive and
negative y'-direction starting from a period length .lamda. shown
in FIG. 5. Through such a decrease, the above-mentioned windowing
effect may be at least partially compensated. It should be noted
that compensation of the "windowing" effect in embodiments only
needs to be applied for the desired range of travel 22, i.e. the
desired behavior of the magnetic field in embodiments has to be
present at locations where a magnetic field sensor may sense the
magnetic field over the range of travel 22.
[0053] Apart from the varying width of the magnetic stripes, the
embodiment of FIG. 5 corresponds to the embodiment of FIG. 2, and
like elements bear the same reference numerals. Modifications and
variations discussed for the embodiment of FIG. 2, for example as
discussed with references 3A to 3D and 4, may also be applied to
the embodiment of FIG. 5, with only the width of stripes 50, 51
changing as explained above. It should be noted that FIG. 5 also
illustrates that a magnet arrangement to the embodiment need not
have a rectangular shape as shown in FIG. 2 for magnet arrangement
24, but may also have a different shape, a hexagon shape as shown
for magnet arrangement 52 of FIG. 5.
[0054] In further embodiments, a width of each or some of the
magnetic stripes additionally or alternatively may vary in the
x'-direction. An embodiment of a corresponding magnet arrangement
62 is illustrated in FIG. 6. Here, the width of stripes 60, 61 on
the one hand decreases in the positive and negative y'-direction
from one stripe to the next, as in FIG. 5, and additionally varies
monotonously in the x'-direction within each stripe. In some
embodiments, this may further serve to limit the windowing effect,
and in particular may limit an influence of a limited size of
magnet arrangement 62 on the sinusoidal shape of the magnetic field
components By', Bz.
[0055] Apart from the discussed varying width of magnetic stripes
60, 61, magnet arrangement 62 of FIG. 6 may be implemented as
discussed previously for magnet arrangement 24 or 52, including
variations and modifications discussed.
[0056] The magnet arrangements discussed previously are in
particular suitable for implementing a linear position sensor
device. Such a sensor device may for example be implemented as
explained with reference to FIG. 1 using a magnetic field sensor
like magnetic field sensor 11. As already mentioned with respect to
FIG. 1, in other embodiments rotational position sensors, for
example angular sensors sensing an angular position, may be used.
For implementing a rotational sensor, essentially the linear travel
path 22 may be "wound" about the centre of rotation, such that the
path (for example travel range 22 discussed previously) forms e.g.
a closed circle. In embodiments where it is not necessary to sense
a full circular movement (for example when only a certain angular
range is of interest), the circle may be opened. A first
possibility to achieve this is to provide the magnetic stripes on a
cylinder barrel of a cylinder rotating about an axis relative to a
magnetic field sensor. A second possibility is to provide the
magnet arrangement on a plane in a circular manner. The directions
like x, y, x', y' mentioned in FIGS. 2, 5 and 6 change accordingly
and in particular are not necessarily straight directions.
[0057] With the second possibility mentioned above, a spiral shape
of the magnet arrangement results. An infinite extension of the
magnet arrangement of a linear sensor as discussed with reference
to FIG. 2 then would result in an internal diameter of the spiral
of 0 and an external diameter of approximating infinity. Values
between 0 and infinity for internal and external diameter
correspond to a limited extension of the magnet arrangement in y
(or y')-direction for a linear sensor as discussed with reference
FIGS. 2, 5 and 6.
[0058] An example for a corresponding magnet arrangement 72
according to an embodiment is illustrated in FIGS. 7. 70 and 71
correspond to alternating magnetic stripes which are wound in a
spiral, and 73 illustrates an example path of a magnetic field
sensor travel range relative to magnet arrangement 72. In the
example of FIG. 7, the spiral shape is such that the pattern formed
by stripes 70, 71 moves "inward" by one period .lamda. with a
rotation of 360.degree. of the spiral.
[0059] For example, the x-direction of FIGS. 2, 5 and 6 may now
correspond to a circumferential direction (for example direction
along path of travel 73), and the y-direction may correspond to a
radial direction (from a centre of rotation towards the outside).
x'- and y'-directions are offset therefrom by a respective angle
corresponding to the above-described angle .tau..
[0060] Compared to the linear case described previously, the
curvature of the magnetic stripes 70, 71 may to some extent
introduce distortions, i.e. for example deviations from a
sinusoidal periodic shape of the relevant magnetic fields depending
on angular position. In some embodiments this may be mitigated by
reducing the width of stripes 70, 71 towards the outside of the
spiral shape shown.
[0061] It should be noted that the spiral shape shown may be
left-handed or right-handed.
[0062] It should also be noted that the widths of magnetic stripes
70, 71 may differ from the widths illustrated in the embodiment of
FIG. 7. As an example, FIG. 8 illustrates a magnet arrangement 82
where magnetic stripes 80, 81 have a greater width than shown in
FIG. 7, and a corresponding spiral makes little more than one turn.
83 denotes a possible path of a magnetic field sensor relative to
magnet arrangement 82. In some cases, a decrease of field strength
in the z-direction (perpendicular to the plane shown in FIGS. 7 and
8) may be lower in case of FIG. 8 than in case of FIG. 7. As can be
seen in FIG. 8, a width of stripes 80, 81 may decrease towards an
outside of the spiral and towards an inside of the spiral in some
embodiments.
[0063] In such angular position sensors using for example magnet
arrangement as illustrated in FIGS. 7 and 8, tolerances or
clearances of the rotational axis may lead to a change of a
distance between a magnetic field sensor and a magnet arrangement,
for example to a change of an air gap (change of the z-position of
the sensor). Similar to what has been explained above for the
linear case, measurements may be robust against variations of the
z-positions by measuring two magnet field components and using a
ratio between the components for determination of the position.
[0064] In some embodiments, a radial component BR (i.e. a component
in a radial direction, e.g. from a center of rotation outwards)
could be used together with Bz, which would correspond to using By
and Bz in the linear case. As explained above, in some embodiments
in the linear case By' (and not By) and Bz are used, which may have
advantages in certain circumstances.
[0065] Therefore, in the angular position sensor case for example
of FIGS. 7 and 8, a component corresponding to By' in the linear
case may be used, which corresponds to a component largely
corresponding to the radial component BR (i.e. direction from the
centre of rotation towards the outside), but also has a small
component of a circumferential field B.psi. (field in the
circumferential direction, for example a direction along path 83).
R and .psi. may for example indicate the polar coordinates in the
plane of FIG. 8, the z-direction being perpendicular thereto and R
being the radial coordinate an .psi. the angular coordinate.
[0066] In some embodiments, a magnetic field sensor senses a magnet
field in one direction in the (R-, .psi.)-plane (plane shown for
example in FIGS. 7 and 8) and a magnetic field perpendicular
thereto (Bz), i.e. perpendicular to the (R-, .psi.-)plane and from
this calculates an angular position, for example rotational angle
of the magnet arrangement or rotation angle of the magnetic field
sensor. In some embodiments, a magnetic field sensor may comprise
respective sensor elements which are sensitive to a respective
desired magnetic field direction in the (R, .psi.)-plane, for
example a vertical Hall sensor with a certain orientation parallel
to a chip edge, wherein the respective chip or package is arranged
at an angle to the magnet arrangement to provide a desired
orientation.
[0067] In some embodiments, the magnetic field sensor, for example
implemented as a sensor chip, may comprise a plurality of sensor
elements which sense magnetic fields in two directions in the (R,
.psi.)-planes, the two directions linear independent from each
other (i.e. being different by an angle which differs from an
integer multiple of 180.degree.). When two such directions are
sensed, any desired direction in the (R, .psi.)-plane may be
calculated based on a linear combination. In such a case, any
desired orientation of a sensor chip could be used as long as two
linear independent directions in the (R, .psi.)-plane may be
sensed. It should be noted that this also applies to the linear
case, where by two linear independent measurements in the x-y-plane
(corresponding to the x'-y'-plane) a magnetic field in any desired
direction in this plane, for example in the y'-direction (By') may
be calculated.
[0068] FIG. 9 illustrates a cross-sectional view of a angular
position sensor device where magnet arrangements as discussed with
reference to FIGS. 7 and 8 or other similar magnet arrangement may
be used. The embodiment of FIG. 9 is only one example for such a
suitable position sensor device, and other implementations are also
possible.
[0069] In the embodiment of FIG. 9, two elements 90, 91 are
provided forming a gap in which a magnetic field sensor 95 is
positioned. In embodiments, elements 90, 91 may be made of a
magnetically soft material, for example magnetically soft steel. A
relative permeability .mu..sub.R of such a magnetically soft
material may be greater than 300, for example greater than 1700 or
greater than 4000. Element 90 in the embodiment of FIG. 9 carries a
magnet arrangement 94, for example a spiral-shaped arrangement as
illustrated and explained with respect to FIG. 7 or 8. In the
embodiment of FIG. 9, element 90 may for example rotate about an
axis 93, and the device of FIG. 9 serves to provide an angular
position of element 90 and therefore a rotation angle of axis 93.
In other embodiments, magnet arrangement 94 may be provided on a
further element. Element 91 may rotate together with element 90 or
may be stationary. Elements 90, 91 in embodiments may shield
magnetic field sensor 95 from external magnetic fields. In
embodiments, the distance between elements 91, 90 at the position
of sensor 95 may be such a magnet field generated by magnet
arrangement 94 is comparatively weak at element 91, such that
element 91 does not significantly influence the magnetic field
generated by magnet arrangement 94.
[0070] The above-described embodiments serve merely as examples,
and in other embodiments other configurations may be used.
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